Conventionally, as this kind of coupling device, there is known, in Published Unexamined Patent Application No. 131855/1993, a coupling device in which: between the left and right wheels there are provided a first coupling passage which transmits the rotation of one of the left and right wheels to the other thereof with increasing speed, and a second-coupling passage which transmits the rotation of one of the wheels to the other thereof with decreasing speed; in both the coupling passages a clutch is interposed respectively; and at the time of cornering when one of the wheels becomes an inner wheel, the clutch for the first coupling passage is engaged, and at the time of cornering when one of the wheels becomes an outer wheel, the clutch for the second coupling passage is engaged so that the outer wheel is positively speeded up as compared with the inner wheel. In this manner, by generating a braking force on the inner wheel side and a driving force on the outer wheel side, the cornering performance is sought to be improved.
By the way, at the time of starting on a slippery road such as on a snowy road or the like, it is being considered to perform a starting assistance by driving the idler wheels by a driving source such as an electric motor or the like. It is desired to obtain a starting assistance function in addition to the above-described cornering control function in that the cornering performance is improved by generating a difference rotation between the left and right wheels.
The present invention has an object of providing a compact and inexpensive coupling device which meets the above-described desire and in which a difference rotation between the right and left wheels can be generated by utilizing the driving source for the starting assistance.